As is well-understood in the art, periodic scatterometry targets are used to obtain accurate measurements of target features. Such targets include massive arrays of uniformly constructed and uniformly spaced periodic features arranged to provide the best possible sensitivity to the measured parameters. Typical prior art example targets include periodic gratings or periodically configured higher dimensional target arrays comprised of a plurality of uniformly spaced and sized metrology features.
In either case such targets have a finite degree of sensitivity. In one typical example, a scatterometry target can be used to, for example, measure a target array (for example and array of 100 nm diameter “dots” or features). Such a scatterometry measurement can attain sensitivity as high as 100 nm±0.8 nm. Although suitable for some present needs, increased target sensitivity is desirable. Moreover, as feature sizes and critical dimensions continue to shrink lithographic processes are under continuing pressure. This will continue for the foreseeable future. Therefore, added sensitivity will continue to be a priority.
Therefore, although such existing processes and tools are suitable for their intended purposes, improvements can be made. The present invention seeks to go beyond the limitations and structural shortcomings of existing technologies.